1. Field of the Invention
The present invention relates to a hydrogen tank filling station as well as to a method of filling a hydrogen tank with hydrogen.
2. Description of the Related Art
Generally, a fuel cell, which generates electrical energy by an electrochemical reaction between hydrogen and oxygen, is supplied with hydrogen as a fuel from a hydrogen tank, which is located near the fuel cell and which stores hydrogen under a high pressure. When the amount of hydrogen that is stored in the hydrogen tank decreases, the hydrogen tank is connected to a high-pressure hydrogen storage tank, which stores hydrogen under a pressure higher than the hydrogen tank. Thus, the hydrogen tank is replenished with hydrogen supplied from the high-pressure hydrogen storage tank. Usually, hydrogen tanks, which are mounted on vehicles powered by fuel cells, are filled with hydrogen at hydrogen tank filling stations.
It is known in the art that when the hydrogen tank is filled with high-pressure hydrogen from the high-pressure hydrogen storage tank, the hydrogen inside the filled hydrogen tank generates heat. The temperature in the hydrogen tank immediately after filling the hydrogen tank is higher than the ambient temperature, and equals or exceeds +70° C., for example. An increased pressure of hydrogen inside the hydrogen tank immediately after filling the hydrogen tank also develops at the high temperature, due to the rise in temperature. Thereafter, when the temperature inside the hydrogen tank drops, so as to be near to the atmospheric temperature, the pressure of hydrogen inside the hydrogen tank also drops to a level that is lower than the hydrogen pressure immediately after completion of filling the hydrogen tank. When the above temperature rise occurs, therefore, the filled hydrogen tank is likely to suffer a shortage of hydrogen.
Japanese Laid-Open Patent Publication No. 2005-69332 discloses, as a method of reducing a temperature rise in the hydrogen tank when thus-filling a hydrogen tank with hydrogen, a hydrogen supply station having a supply pipe for supplying hydrogen to a hydrogen tank on a vehicle from a plurality of high-pressure hydrogen storage tanks, which store the hydrogen under a plurality of different pressure stages. The hydrogen supply station also has a cooling means disposed within the supply pipe for cooling hydrogen as it flows through the supply pipe. The temperature in the hydrogen tank is detected for enabling a feedback control. The hydrogen tank is filled with hydrogen, which is cooled by the cooling means, depending on the detected temperature inside the hydrogen tank.
According to the disclosed hydrogen supply station, the temperature inside the hydrogen tank is monitored and detected to enable a feedback control, so as to cause the cooling means to cool the hydrogen depending on the detected temperature, whereupon the hydrogen tank is filled with cooled hydrogen. Consequently, the number of components, such as the detecting means, valves, etc., tends to be large, and the control process therefor is complex.